I'm not sure. The thing is that Q1 drain on both ch. was shorting to ground
once I start tightening it to the sink. Strange that was not the case with Q4-
it stayed insulated from the sink no matter how tight it was. I know that as
my audio gnd is separated from the safety gnd by 10R-2W II 100n NPO.
My meter showed 0ohm Q1 (tightend to sink) to chassis and ~10ohm Q4 to chassis.

I have some graphite to240 pads. I purchased them (years ago) because of their astoningshly low thermal resistance.
Unfortunaly they are conductive. It was written on the specs..